Hi Sue,
If you are an Office 365 subscriber, you will not get the product key. We use our Office 365 accounts to activate Office desktop application which we download from Office 365. When you open Office for Mac 2011 for the first time, there will be an option for you to enter your Office 365 account. Please enter your account and password to activate it.
If you still have concerns, please reply to me with the Office 365 plan you have purchased.
Thanks,
August